The present invention relates generally to the field of communication, and, more particularly, to communication devices having a co-located transmitter and receiver in which the transmitter can interfere with the operation of the receiver.
Wireless communicators are being used in ever increasing numbers for voice calls, data calls, facsimile transfer, Internet access, paging, and other personal organization features such as calendar management or even travel directions via the Global Positioning System (GPS). GPS is a worldwide navigation system that is based on a constellation of satellites, which are used as reference points to calculate positions on earth. More specifically, GPS uses a technique known as xe2x80x9ctriangulationxe2x80x9d in which the GPS receiver determines the distance to particular satellites using the travel time of the GPS signals transmitted by those satellites. In addition to determining the distance to a transmitting satellite, the receiver may also obtain information from a GPS signal that indicates the position of the transmitting satellite in space. Finally, the receiver may correct for delay that a GPS signal can experience in traveling through the atmosphere.
As used herein, the term xe2x80x9cwireless communicatorxe2x80x9d can include a cellular radiotelephone with a multi-line display, a Personal Communications System (PCS) terminal that may combine a cellular radiotelephone with data processing, facsimile and data communications capabilities, a Personal Digital Assistant (PDA) that can include a radiotelephone, pager, Internet/intranet access, Web browser, organizer, calendar and/or a GPS receiver, and conventional laptop and/or palmtop receivers that include radiotelephone transceivers. Wireless communicators also may be referred to as xe2x80x9cpervasive computingxe2x80x9d devices.
Wireless communicators that include both a cellular radiotelephone and a GPS receiver, for example, may be susceptible to interference between the cellular phone transmitter circuitry and the GPS receiver circuitry. With reference to FIG. 1, a wireless communicator 22 is illustrated in which a GPS receiver 24 and a cellular transceiver 26 are co-located. Because the wireless communicator 22 may be relatively small and have minimal separation between the GPS antenna 28 and the cellular antenna 32, it is not uncommon for radio frequency (RF) signals transmitted from the cellular transceiver 26 to couple from the cellular antenna 32 to the GPS antenna 28. As a result, this unwanted interference from the cellular transceiver 26 may inhibit operation of the GPS receiver 24.
In addition to interfering with the reception and decoding of a GPS signal while the cellular transceiver 26 is transmitting, operation of the GPS receiver 24 may also be disrupted while the cellular transceiver 26 is idle or is in a receive mode. As shown in FIG. 1, an automatic gain control (AGC) module 34 is typically used to adjust the gain of the signal received through the GPS antenna 28 to a power level suitable for processing by the GPS receiver 24. The coupling of an RF signal from the cellular antenna 32 to the GPS antenna 28, however, generally increases the strength of the signal applied to the input of the GPS receiver 24. Therefore, the AGC module 34 may reduce the gain applied at a multiplier 36 when the cellular transceiver 26 transmits. When the cellular transceiver 26 transitions to an idle mode or a receive mode for the particular communication protocol that it is implementing, the gain applied by the AGC module 34 may be insufficient to provide a suitable signal power level at the input of the GPS receiver 24. The AGC module 34 may thus increase the gain in response to the lower power level of the signal from the GPS antenna 28, but the cellular transceiver 26 may eventually transition back into the transmit mode, thereby causing the cycle to repeat.
Thus, it can be difficult to maintain operation of the GPS receiver 24 when it is co-located with a cellular transceiver 26. When the cellular transceiver 26 is transmitting, the transmitted signal can interfere with the reception and decoding of a GPS signal by the GPS receiver 24. When the cellular transceiver 26 is idle or is receiving a cellular signal, the GPS signal received at the GPS receiver 24 may be too weak to decode because the gain applied by the AGC module 34 has been reduced from its normal operating value due to the prior interference from the signal transmitted by the cellular transceiver 26.
Consequently, a need exists for improved communication devices in which the operation of a receiver can be maintained notwithstanding interference from a co-located transmitter.
It is therefore an object of the present invention to provide improved communication devices in which a receiver is co-located with a transmitter and is susceptible to interference therefrom.
It is another object of the present invention to provide systems and methods that can be used to maintain operation of a receiver in a communication device that is subject to interference from a co-located transmitter during periodic transmission intervals.
These and other objects, advantages, and features of the present invention may be provided by systems and methods that can be used to maintain the operation of a receiver co-located with a transmitter in a communication device and susceptible to interference therefrom by anticipating the intervals during which the transmitter is active (i.e., transmitting) and then desensitizing the receiver during that interval. Although the receiver may operate in a reduced capacity due to periodic desensitization, the adverse effects of interference from the signal generated by the transmitter can be avoided. For example, interference from the transmitter can cause variables, such as the gain applied by an AGC module at the receiver input, to deviate from a normal operating or steady state value, which must then be recovered when the interference from the transmitter ceases.
In accordance with an illustrative embodiment of the present invention, control logic is used to monitor a signal generated by the transmitter. By monitoring the aforementioned signal, the control logic is able to anticipate the beginning of the transmission intervals and generate a control signal that identifies or corresponds to the intervals in which the transmitter is active or transmitting. This control signal is then supplied to an automatic gain control module to maintain the gain applied at the input of a second receiver at or above its current level. Advantageously, if the signal transmitted by the transmitter is coupled to the second receiver thereby causing interference, then the automatic gain control module will not reduce the gain applied due to the enhanced signal strength resulting from the interference. When a transmission interval completes, the gain provided by the automatic gain control module is therefore at a proper level for normal or steady state operation.
In accordance with another illustrative embodiment of the invention, control logic is. used to anticipate the beginning of a transmission interval; however, the control signal generated in response thereto is used to drive a switch that electrically isolates the second receiver from an antenna associated therewith during the transmission interval.
In accordance with still another illustrative embodiment of the invention, a communication protocol (e.g., a protocol based on time division multiple access (TDMA) technology) program is used that anticipates the active or transmission intervals of the transmitter and generates a control signal via a processor to desensitize the receiver during these intervals.
The present invention can allow, for example, a GPS receiver, co-located in a cellular phone terminal, to operate almost simultaneously with a TDMA transmitter. Heretofore, in an application where there is minimal antenna isolation between the GPS receiver antenna and the cellular phone antenna, operation of the GPS receiver may be severely hampered due to disruption of the gain applied by an automatic gain control module at the input of the GPS receiver.